The present invention relates to a mobile terminal radio calling system having communication functions in both a high-speed mobile communication mode and a low-speed mobile communication mode in a mobile communication system using both the modes and, more particularly, to a radio calling system which notifies a mobile subscriber of the reception of a terminating call even if the mobile terminal is moving at a high speed and set in the low-speed mobile communication mode.
As a conventional mobile communication system of this type, for example, Japanese Patent Laid-Open No. 3-92023 discloses a system which can ensure communication when the moving speed of a mobile radio unit exceeds a predetermined speed. In this system, a dedicated calling radio base station which covers all the service areas respectively covered by a plurality of radio base stations is connected to a gateway switching unit through a transmission line. The dedicated calling radio base station is used to call a mobile radio unit upon reception of a terminating call when the mobile radio unit in a standby state in the mobile communication system is moving at a speed equal to or higher than a speed determined in terms of system design, and the transmission of a position registration signal is kept stopped. With this operation, even if a mobile radio unit is mounted in a vehicle, e.g., an automobile, which moves at a high speed, a terminating call is ensured by the use of the dedicated calling radio base station which covers a wide area.
Japanese Patent Laid-Open No. 1-144826 discloses a system in which a dedicated calling radio base station can reliably call a mobile radio unit in the process of moving at a high speed. In this system, when the communication quality of one of a plurality of channels through which a plurality of radio base stations are exchanging the same communication contents with a mobile radio unit becomes a predetermined value or less, this channel is switched to another channel of another radio base station which satisfies the predetermined communication quality. With this operation, the communication through the old channel is stopped, and the same communication contents can be communicated through a plurality of channels including the new channel without a short break.
FIG. 13 shows a system configuration based on the above two prior arts. As described above, both the prior arts disclosed in Japanese Patent Laid-Open Nos. 3-92023 and 1-144826 aim at preventing a deterioration in communication quality and a state in which a calling operation cannot be performed, which are caused when a mobile terminal under communication moves at a high speed in mobile communication using micro-cell zones satisfying the communication quality requirement, and ensuring a calling function.
In order to achieve the above object, in the arrangement shown in FIG. 13, one of radio base stations (radio ports) 12a to 12e, or a gateway switching unit 13 detects that any radio base station that can perform communication cannot be specified while a mobile terminal 11 is moving at a high speed. The radio base stations 12a to 12e and the gateway switching unit 13 shift the registration division of the identification information of the mobile terminal 11 to a wide-area calling registration division. When a terminating call addressed to the mobile terminal 11 is received, the mobile terminal 11 is called by using a dedicated calling radio base station 14.
However, the above prior arts have the following problems. In the above prior arts, a dedicated calling radio base station must be installed to call a mobile terminal moving at a high speed. Manufacturing and installation costs are required to install a dedicated calling radio base station. In addition, in order to control the dedicated calling radio base station, extra radio channel control and protocol control are required.
Both the prior arts aim at preventing a deterioration in communication quality and interruption of the calling function, which may be caused when a mobile terminal is moving at a high speed. For this reason, according to the conventional systems described above, in a mobile communication system including low-speed communication mode/macro-cell zone mobile terminals and high-speed communication mode/macro-cell zone mobile terminals, when a low-speed mobile communication mode or low-speed mobile communication mode zone mobile terminal moves at a high speed, it is difficult to perform a calling operation or continue communication. With a high-speed communication mode mobile terminal, a calling operation and continuation of speech communication can be easily ensured even under the present situations regardless of the moving speed of the terminal.
Consider a mobile terminal capable of performing communication in both the low-speed mobile communication mode/macro-cell zone and the high-speed mobile communication mode/macro-cell zone. If this mobile terminal is set in the high-speed mobile communication mode, a calling operation and continuation of speech communication can be easily ensured regardless of the moving speed.
Considering the current call rate system, communication using the high-speed mobile communication mode is higher in reference call rate and telephone charge than communication using the low-speed mobile communication mode. For this reason, the low-speed mobile communication mode has attracted a greater deal of attention. That is, a reduction in charge can be achieved by setting the low-speed mobile communication mode as often as possible except that the user waits for an urgent call.
Demands have therefore arisen for a system which can eliminate the difficulties in calling and continuing speech communication when a mobile terminal in the low-speed mobile communication mode is moving at a high speed. That is, if an originating subscriber is notified of at least information about high-speed movement when a mobile terminal set in the low-speed mobile communication mode is moving at a high speed, a radio selective calling operation corresponding to the function of a pager can be realized.